The present invention relates to apparatus and system for lubricating the bearings of cutting rollers supported on the pivots of a roller bit. In this system and apparatus the roller bit has an inner cavity or chamber filled with a noncompressible flushing liquid under a feed pressure and means for circulating the flushing liquid through the bearings.
Lubricating the bearings in apparatus of this type by noncompressible lubricant is not new per se. A typical prior art lubricating system is illustrated in French Pat. No. 1,466,378. This system, however, has some drawbacks and shortcomings. For example, in order to prevent the flushing liquid mixed with the drilling mud from entering from the outside environment into the bearing cavity and causing detrimental wear, a gasket or seal must be provided on the side of the bearing cavity facing the roller bit. In drilling operations, the drilling apparatus is subjected to heavy shock loads resulting in quick wear and deterioration of the gasket or seal rendering it inoperative or useless after a relatively short operating period. Failure of the gasket or seal allows flushing liquid to pass through the bearings of the cutting roller and the deposits carried along with the flushing liquid such as the wear causing drilling mud enter the bearing. This produces premature bearing wear and failure. Additionally it has been found that with this prior system, special lubricant reservoirs must be provided which greatly increase the manufacturing cost of the roller bit. This also results in a comparatively expensive maintenance program, warehousing of the special lubricants and regular replenishment of the lubricant reservoir. Moreover, the known systems described above have the further disadvantage that the friction heat is removed only by the flushing liquid around the outside of the cutting rollers through the wall of the cutting roller so that detrimental overheating and corresponding damage to the bearings during operation often result.
It is an object of the present invention to provide an improved system and apparatus for lubricating bearings of the cutting rollers characterized by novel features of construction and arrangement which eliminates the need for packing the roller bit with lubricant as well as eliminating means for sealing the bearing cavity from the outside. It is also an object to provide a lubricating system and apparatus which is easy and economical to manufacture and provides a long service life of the cutting rollers by reducing the heat generated during operation and thereby eliminating premature bearing wear and friction.